Novel Co(II) and Cu(II) coordination complexes constructed from pyrazole-acetamide: Effect of hydrogen bonding on the self assembly process and antioxidant activity

Article abstract of DOI:10.1016/j.jinorgbio.2018.11.006

In the present study, two pyrazole-acetamide derivatives namely N?(2?aminophenyl)?2?(5?methyl?1H?pyrazol?3?yl) acetamide (L1) and (E)?N?(2?(1?(2?hydroxy?6?methyl?4?oxo?4H?pyran?3?yl)ethylideneamino)phenyl)?2?(5?methyl?1H?pyrazol?3?yl) acetamide (L2) have been synthesized and characterized by infrared spectrophotometry (IR), nuclear magnetic resonance spectroscopy (NMR) and electrospray ionization-mass spectrometry (ESI-MS). Two coordination complexes of L1 and L2, namely [Co(L1)₂(EtOH)₂]·Cl₂ (1) and [Cu(L2)]·H₂O (2), respectively have been synthesized and characterized by elemental analysis and spectroscopic studies. The solid state structure of these two complexes was established by single crystal X-ray crystallography. In complex 1, the amide O and pyrazole N atoms of two molecules of L1 take part in coordination with octahedral Co(II) ions, the remaining two coordination sites being occupied by two EtOH molecules leading to a N₂O₄ coordination environment. On the other hand, the imine N atoms, pyrazole N and O atoms of the 2?hydroxy?6?methyl?4H?pyran?4?one function present in L2 are involved in coordination with Cu(II) ions, resulting in a distorted square planar geometry displaying a N₂O₄ chromophore, in complex 2. The crystal packing analysis of 1 and 2, revealed 1D and 2D supramolecular architectures respectively, via various hydrogen bonding interactions, which are discussed in the present account. Furthermore, the antioxidant activity of the ligands and their complexes were determined in vitro by 1,1?diphenyl?2?picrylhydrazyl (DPPH), 2,2′?azino?bis(3?ethylbenzothiazoline?6?sulphonic acid (ABTS) and ferric reducing antioxidant power (FRAP), showing that the ligands L1 and L2 and complexes 1 and 2 present significant antioxidant activity.

Full text of DOI:10.1016/j.jinorgbio.2018.11.006

Accepted Manuscript
Novel Co(II) and Cu(II) coordination complexes constructed from
pyrazole-acetamide: Effect of hydrogen bonding on the self
assembly process and antioxidant activity
Karim Chkirate, Saad Fettach, Khalid Karrouchi, Nada Keira
Sebbar, El Mokhtar Essassi, Joel T. Mague, Smaail Radi, My El
Abbes Faouzi, N.N. Adarsh, Yann Garcia
PII:
S0162-0134(18)30550-6
DOI:
Reference:
https://doi.org/10.1016/j.jinorgbio.2018.11.006
JIB 10593
To appear in:
Journal of Inorganic Biochemistry
Received date:
Revised date:
Accepted date:
12 September 2018
29 October 2018
8 November 2018
Please cite this article as: Karim Chkirate, Saad Fettach, Khalid Karrouchi, Nada Keira
Sebbar, El Mokhtar Essassi, Joel T. Mague, Smaail Radi, My El Abbes Faouzi, N.N.
Adarsh, Yann Garcia , Novel Co(II) and Cu(II) coordination complexes constructed from
pyrazole-acetamide: Effect of hydrogen bonding on the self assembly process and
antioxidant activity. Jib (2018), https://doi.org/10.1016/j.jinorgbio.2018.11.006
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ACCEPTED MANUSCRIPT
NovelCo(II) and Cu(II) coordinationcomplexes constructedfrom pyrazole-
acetamide: Effect of Hydrogen bonding on the Self Assembly process and
antioxidant activity
a
b
c
a
Karim Chkirate , Saad Fettach , Khalid Karrouchi , Nada Keira Sebbar , El Mokhtar
a
d
e
b
f
Essassi , Joel T. Mague , Smaail Radi , My El Abbes Faouzi , N. N. Adarsh , Yann
f,*
Garcia
a
LCOH, Département de Chimie, Faculté des Sciences, Université Mohamed V, BP1014, Rabat
10100, Morocco.
b Laboratory of Pharmacology and Toxicology, Pharmacokinetic Research Team, Faculty of Medicine
and Pharmacy, University Mohammed V, Rabat, Morocco
c LNCM, Direction du Médicament et de la Pharmacie, Ministère de la Santé, BP 6206, Rabat 10100,
Morocco.
d Department of Chemistry, Tulane University, New Orleans, LA 70118, USA.
e
LCAE, Département de Chimie, Faculté des Sciences, Université Mohamed I, BP 524, 60 000 Oujda,
Morocco
f Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Place L. Pasteur
1, 1348 Louvain-la-Neuve, Belgium.
*Corresponding author: yann.garcia@uclouvain.be; Tel: +32 10 47 28 26, Fax: +32 10 47 23 30
1

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A B S T R A C T:
In the present study, two pyrazole-acetamide derivatives namely N-(2-aminophenyl) -2- (5-
methyl-1H-pyrazol-3-yl) acetamide (L1) and (E)-N-(2-(1-(2-hydroxy-6-methyl-4-oxo-4H-
pyran-3-yl)ethylideneamino)phenyl)-2-(5-methyl-1H-pyrazol-3-yl) acetamide (L2) have been
synthesized and characterized by infrared spectrophotometry (IR), nuclear magnetic
resonance spectroscopy (NMR) and electrospray ionization-mass spectrometry (ESI-MS).
Two coordination complexes of L1 and L2, namely [Co(L1)2(EtOH)2]·Cl2 (1) and
[Cu(L2)]·H2O (2), respectively have been synthesized and characterized by elemental
analysis and spectroscopic studies. The solid state structure of these two complexes were
established by single crystal X-ray crystallography. In complex 1, the amide O and pyrazole
N atoms of two molecules of L1 take part in coordination with octahedral Co(II) ions, the
remaining two coordination sites being occupied by two EtOH molecules leading to a N2O4
coordination environment. On the other hand, the imine N atoms, pyrazole N and O atoms of
the 2-hydroxy-6-methyl-4H-pyran-4-one function present in L2 are involved in coordination
with Cu(II) ions, resulting in a distorted square planar geometry displaying a N2O4
chromophore, in complex 2. The crystal packing analysis of 1 and 2, revealed 1D and 2D
supramolecular architectures respectively, via various hydrogen bonding interactions, which
are discussed in the present account. Furthermore, the antioxidant activity of the ligands and
their complexes were determined in vitro by 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-
azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) and ferric reducing antioxidant
powerꢀ(FRAP), showing that the ligands L1 and L2 and complexes 1 and 2 had significant
antioxidant activity.
Keywords: Pyrazole; Crystal engineering; Coordination Complexes; Hydrogen Bonding;
Antioxidant activity.
2

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1. Introduction
Pyrazole derivatives are biologically active heterocyclic compounds [1]. This substance class
has been the topic of numerous pharmaceutical studies being used for their medicinal
properties such as anti-inflammatory [2-3], antimicrobial [4], antiviral [5], analgesic [6].
antitumoral [7], catecholase [8], and even as insecticides [9]. Some of the specific examples,
including pyrazoles, inhibit the secretion of amyloid responsible for Alzheimer's disease [10].
Other examples are pyrazolopyrimidines [11] reported as estrogen receptor antagonists. In
particular, pyrazolylacetamide derivatives have been evaluated for their in vitro activity as
antimycobacterial agents against Mycobacterium smegmatis and as anti-cytotoxic anti-
tuberculosis agents [12] and also as anti-glycemic agents [13]. They also have therapeutic
properties for the treatment of Cryptosporidium parasites [14]. Their metal complexes have
proven antimicrobial activities [15] too and may also have applications in catalysis [16].
Nitrogen systems have attracted more attention in recent years because of their interesting
properties in coordination chemistry [17-18], particularly the synthesis of iron complexes due
to their spin crossover [19] and their molecular properties [20]. This ability is mainly due to
the presence of hybrid sp2 nitrogen donors [21] with the involvement, in some cases, of other
donating sites such as oxygen and sulfur atoms [22].
Reactive oxygen species (ROS) are chemically reactive chemical species containing oxygen.
However, the excess production of ROS can become toxic to the major components of the
cell, lipids, proteins and nucleic acids, and can give rise to oxidative stress that can be
involved in various pathologies [23, 24].
Antioxidant pharmacotherapy has appear as a tool to minimize the bimolecular damage
caused by the attack of ROS to these vital constituents of living organisms, and therefore
synthetic antioxidants have received much attention from the pharmaceutical viewpoint [3].
However, a significant number of research teams have concentrated on the role of complexes
as antioxidants [25-26].
In order to search for new ligand candidates for assemblies of metal complexes, we
considered the case of pyrazole acetamide ligands with O and N donor atoms. These
molecules are particularly interesting as ligands for the construction of polynuclear complexes
as models for bioinorganic systems [27-28]. In this work, we describe the synthesis of
derivatives of pyrazole functionalized with acetamides and the crystal structure of two novel
Co(II) and Cu(II) coordination complexes derived from these ligands, namely N-(2-
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aminophenyl) -2- (5-methyl-1H-pyrazol-3-yl) acetamide (L1) and (E)-N-(2-(1-(2-hydroxy-6-
methyl-4-oxo-4H-pyran-3-yl)ethylideneamino)phenyl)-2-(5-methyl-1H-pyrazol-3-yl)
acetamide (L2) (Figure 1). The antioxidant properties of the ligands and their complexes are
evaluated in vitro using DPPH and ABTS radical scavenging methods and Ferric Reducing
Antioxidant Powerꢀ(FRAP).
2. Experimental
2.1. General methods
Melting points were measured using a Büchi B-545 digital capillary melting point apparatus
and used without correction. Reactions were checked with TLC using aluminum sheets with
silica gel 60 F254 from Merck. IR spectra were recorded on a Perkin-Elmer VERTEX 70 FT-
-1
1
IR spectrometer covering field 400–4000 cm . H and 13C NMR spectra were recorded in
DMSO-d6 on a Bruker spectrometer (300 MHz). Chemical shifts are expressed in ppm by
using tetramethylsilane (TMS) as internal reference. Mass spectra were collected using an
API 3200 LC/MS/MS system, equipped with an ESI source. Chemical reagents were
purchased from Fluka, Sigma and Aldrich chemicals.
2.2. Synthesis
2.2.1. Synthesis of (Z)-4-(2-oxopropylidene)-4,5-dihydro-1H-benzo[b][1,4]diazepin-2(3H)-
one
In the xylene (80 mL), 0.02 mol (3.36 g) of dehydroacetic acid and 0.04 mol (4.32 g) of o-
phenylenediamine were refluxed for 4h. Next, the precipitated product was filtered under
reduced pressure and then recrystallized in ethanol. Yield: 75%; M.p (°C): 236-238; IR (ATR,
-1
v(cm )) : 1671, 1607, 1575; 1H-NMR (300 MHz, DMSO-d6, δ(ppm)): 2.00 (s, 3H, CH3); 3.00
(s, 2H, -CH2); 5.20 (1H, s); 7.10 (4H, m); MS: m/z = 216 (M+H)+.
2.2.2. Synthesis of N-(2-aminophenyl)-2-(5-methyl-1H-pyrazol-3-yl) acetamide (L1)
2 g of (Z)-4-(2-oxopropylidene)-4,5-dihydro-1H-benzo [b] [1,4] diazepin-2 (3H)-one and
stoichiometric amount of hydrazine were refluxed in ethanol (40 mL) for 2h. After
concentration of the solvent volume to 20 mL, the solution was allowed to stand; the
precipitate formed was filtered off and then recrystallized in ethanol. A single crystal was
-
obtained after recrystallization from ethanol. Yield: 80%; M.p (°C): 170-172; IR (ATR, v(cm
1
1)) : 3000-3400 (NH,NH2), 1737 (C=O); 1655 (C=N); H-NMR (300 MHz, DMSO-d6,
δ(ppm)): 2.51 (s, 3H, CH3), 2.20 (s, 2H, CH2), 4.86 (s, 2H, NH2), 5.94 (s, 1H, H-pyrazole),
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6.52-7.16 (m, 5H, H-Ar), 9.25 (s, 1H N-H (amide), 12.24 (s, 1H, NH-pyrazole); MS: m/z =
230 (M+H)+.
2.2.3. Synthesis of (E)-N-(2-(1-(2-hydroxy-6-methyl-4-oxo-4H-pyran-3-yl) ethylideneamino)
phenyl) -2- (5-methyl-1H-pyrazol) -3-yl) acetamide (L2)
To a solution of 5 mmol of N-2-aminophenyl-5-methyl-pyrazol-3-yl acetamide in ethanol (60
mL), 5 mmol of dehydroacetic acid solubilized in ethanol was slowly added. After 24h
stirring at room temperature, the formed precipitate was filtered, washed with ethanol and
-1
dried under vacuum. Yield: 85%; M.p. (°C) = 204-206; IR (ATR, v(cm )) : 3390 (OH),
1
3203-3145 (NH), 1700-1710 (C=O), 1590-1610 (C=N); H NMR (300 MHz, DMSO-d6,
δ(ppm)): 2.14 (s, 3H, CH3); 2.37 (s, 3H, CH3); 2.51 (s, 3H, CH3); 3.33 (s, 2H, CH2); 5.81 (s,
1H, H4-pyrazole); 5.84 (s, 1H, pyrone); 7.39-7.55 (m, 4H, phenyl); 9.21 (s, 1H, NH-CO);
12.17 (s, 1H, NH-pyrazole); 15.49 (s, 1H, OH); MS: m/z = 380.4 (M+H)+.
2.2.4. Synthesis of [Co(L1)2(EtOH)2]·Cl2 (1)
L1 (14.4 mg, 0.07 mmol, 2 equiv) was dissolved in ethanol (5 mL). CoCl2∙6H2O (7.5mg,
0.04mmol, 1 equiv) was dissolved in ethanol (5mL) and added to the above solution of L1.
The resulting light brown solution was left at room temperature. Single crystals were obtained
by slow evaporation of a clear light brown solution of the reaction mixture after 24 h. Yield:
48%.
2.2.5. Synthesis of [Cu(L2)]·H2O (2)
L2 (80 mg, 0.25 mmol, 1 equiv) was dissolved in MeOH (5 mL). CuSO4∙5H2O (62.4mg, 0.25
mmol, 1 equiv) was dissolved in water (5 mL) and added to the L2 solution above. The
resulting solution was stirred and warmed slightly. After a few moments, a dark green
precipitate was deposited. The precipitate is filtered and then recrystallized from acetonitrile
and left at room temperature. Dark green single crystals were obtained by slow evaporation of
the reaction mixture after 24 hours. Yield: 30%
2.3. X-ray analysis
X-ray single-crystal data were collected on single crystals using Mo Kα (λ = 0.7107 Å)
radiation on a Bruker SMART APEX diffractometer equipped with CCD area detector. Unit
cell refinement data reduction (SAINT) and structure solution as well as refinement
(SHELXL) [29] were carried out using the software package of SMART APEX. The
structures 1 and 2 were solved by direct method and refined in a routine manner. In both
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structures, non-hydrogen atoms were treated anisotropically. In compound 1, hydrogen atoms
were geometrically fixed. On the other hand in 2, hydrogen atoms were located on a
difference Fourier map and refined. Molecular graphics were generated by using the softwares
MERCURY 3.9 [30] and POV-Ray. The details of the X-ray crystal data and the structure
solution as well as the refinement are given in Table 1. CCDC 1853218 and 1853219 for 1
and 2, respectively contain the supplementary crystallographic data for these compounds, and
can be obtained free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
2.4. Antioxidant activity
2.4.1. DPPH radical scavenging activity
The radical-scavenging activity of each synthesized compounds was evaluated on the basis of
its activity in scavenging the stable DPPH radical, according to the method described by Li et
al. [31]. In this procedure, 2 ml of a 4 % solution of DPPH radical in methanol (w/v) was
mixed with 500 μl of sample solutions at different concentrations (31-2000 µM).
The scavenging capacity was determined spectrophotometrically after 30 min of incubation
by monitoring the decrease of the absorbance at 517 nm. Lower absorbance of the reaction
mixture indicates higher free radical scavenging activity. Ascorbic acid was used as standard.
The percent DPPH scavenging effect was calculated using the following equation:
% of scavenging = [(Ac - At)/Ac] x100
Where Ac is the absorbance of the control sample (DPPH solution without test sample) and
At is the absorbance of the test sample (DPPH solution + test compound). Tests were
performed in triplicate, and the results were averaged.
2.4.2. ABTS radical scavenging activity
The ABTS free radical-scavenging activity of synthesized compounds was estimated using
the method described by Re et al. [32]. The ABTS radical cation was produced by reacting
ABTS with potassium persulfate. The blue-green ABTS was produced through the reaction
between 7mM ABTS and 70mM potassium persulfate in water. The mixture was stored at
room temperature in the dark for 16 h prior use. The ABTS solution was then diluted with
80% methanol to obtain an absorbance of 0.700 ± 0.005 at 734 nm. One hundred microliters
of sample solutions at 1 mM were added to 2 mL of ABTS solution and the absorbance was
recorded at 734 nm after 1 min incubation at room temperature. This was compared to the
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blank where 200 µL of the methanol was added to 2 mL of ABTS solution. A standard curve
was obtained by using Trolox reference solution at various concentrations. The scavenging
activities of different concentrations of synthesized compounds vs. ABTS radical were also
measured to calculate the IC50, and the procedure was similar to the DPPH scavenging
method described above. The test was carried out in triplicate and IC50 values were reported
as means ± SD.
% Inhibition = (Ac - At/Ac) / 100
Where Ac is the absorbance of the control and At is the absorbance in the presence of the
samples or reference. The control did not contain compound or standard.
2.4.3. Ferric Reducing/Antioxidant Power (FRAP) Assay
The ferric-reducing capacity of the ligands and complexes was investigated by using the
potassium ferricyanide-ferric chloride method with some modifications [33]. Briefly, the
sample (1 mL) at 1 mM/L was mixed with 2.5mL of phosphate buffer (0.2M, pH 6.6) and
2.5mL of 1% potassium ferricyanide. The mixture was then incubated at 50 °C for 20 min to
reduce ferricyanide into ferrocyanide. A portion (2.5 mL) of trichloroacetic acid (10 %) was
added to the mixture which was then centrifuged at 3000 rpm for 10 min. Finally, 2.5mL of
the supernatant was mixed with 2.5mL of distilled water and 0.5mL FeCl3 solution (0.1%,
w/v), and the absorbance was measured at 700 nm. Increased absorbance values indicate a
higher reducing power. The results were expressed as ascorbic acid equivalent per mM of
compound (µM/mM comp).
3. Result and discussion
3.1. Synthesis of pyrazole-acetamide ligands L1 and L2
Our strategy was to develop a simple, high-yield, synthetic procedure in a few steps to prepare
the desired acetamide derivatives. The development of the synthesis of L1 and L2 is given in
Scheme 1.
The major product 3 [34] was produced in good yield by condensation of o-phenylenediamine
with dehydroacetic acid (DHA) in refluxing xylene for 4 h. The second step was to react on
product 3 hydrazine monohydrate as a reagent in stoichiometric amount in ethanol, reflux for
2h to give the pyrazole-acetamide L1 ligand in good yield [35]. The third step was to react on
L1 DHA in ethanol at room temperature for 24h to afford the pyranylpyrazole acetamide
ligand L2, again in good yield (Scheme 1).
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3.2. Synthesis of coordination complexes 1 and 2
The crystallization of coordination compounds obtained the reaction of pyrazole-acetamide
ligand L1 and CoII on one hand in an ethanolic solution (metal / ligand ratio 1:2) and the
reaction of pyranyl pyrazole acetamide ligand L2 with CuII on the other hand in an aqueous
methanolic solution (metal / ligand ratio 1:1), followed by recrystallization in acetonitrile,
afforded single crystals of two coordination complexes [Co(L1)2(EtOH)2]·Cl2 (1) and
[Cu(L2)]·H2O (2).
3.3.Description of the crystal structures of the complexes [Co(L1)2(EtOH)2]·Cl2 (1) and
[Cu(L2)]·H2O(2)
3.3.1. [Co(L1)2(EtOH)2]·Cl2 (1)
Single crystal X-ray diffraction analysis has shown that complex 1 crystallizes in
centrosymmetric triclinic P1 space group (Table 1). The crystal structure of 1 can be
described as a chloride inclusion coordination complex of Co(II). The asymmetric unit
comprises one half of Co(II) (sitting on an inversion center), one molecule of L1 and EtOH
(both being coordinated to Co(II) and are around an inversion center) and one chloride
counter anion (also found around an inversion center). Therefore the remaining ligand L1 and
the EtOH molecule for the coordination with Co(II) were generated by the symmetry
inversion center present on the Co(II) atom. The Co(II) metal center exhibits distorted
octahedral geometry [N–Co–O = 87.78(4)–92.22(4)°; O–Co–O = 88.89(4)–91.11(4)°]
with a CoN2O4 chromophore; the equatorial positions are coordinated by two molecules of
ligand L1 through the imine N atoms of pyrazole and O atoms of amide functionalities. Such
coordination affords a stable six membered ring involving the Co(II) metal center and the
ligand, due to the chelation effect of L1. The axial positions of Co(II) are occupied by O
atoms of EtOH molecules. In the crystal structure, the ligand moiety displays a non-planar
conformation as expected, in which the pyrazole and aromatic rings are away from a torsion
angle of ~ 65.63° from each other. In fact such ligand conformation affords stability to the
coordination complex, supported by intra-molecular hydrogen bonding interactions involving
the –NH2 and pyrazole functionalities [N–H∙∙∙N = 2.9801(18)Å; N–H–N = 175°]. The
coordination complex 1, was self-assembled via hydrogen bonding comprising of the lattice
included Cl– anion, amide N–H=O, amine –NH2 and hydroxyl –OH via O–H∙∙∙Cl and N–
H∙∙∙Cl interactions [O–H∙∙∙Cl = 3.0575(12)Å, O–H–Cl = 168°; N–H∙∙∙Cl = 3.1468(14)-
3.3779(14)Å, N–H–Cl = 153-175°] (Table 2). Such self-assembly of 1, through the
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occluded Cl– resulted in a one dimensional hydrogen bonded chain, which can be seen along
the crystallographic axis “a”. Further these chains are packed in parallel fashion supported by
a weak C–H∙∙∙π(ring) interaction (Figure 2), which resulted in a 2D sheet structure, with the
encapsulation of Cl– within the void space. Interestingly such 2D sheets are further assembled
in top of each other in an offset fashion, with the support of offset π∙∙∙π stackings between
pyrazolyl rings with centroid...centroid distances of 3.4976(19)Å.
3.3.2. [Cu(L2)]·H2O(2)
Dark red-violet colored column shaped single crystals of 2 crystallized in a centrosymmetric
triclinic P1 space group (Table 1). The asymmetric unit consists of two crystallographically
independent molecules of coordination complex and a lattice included water molecule. Each
complex molecules contains a Cu(II) metal center and one molecule of ligand coordinated to
the metal center. The Cu(II) metal center shows distorted square planar geometry [N–Cu–O
= 89.18(5)-91.81(5)°; N–Co–N = 84.68(5)- 94.14(5)°] having a four coordination with
CuN2O2 coordination environment. In the crystal structure, the ligand L2 showed reasonable
non-planarity which is easily confirmed from the torsion angle between the aromatic ring and
pyrazole ring, and the aromatic ring and 2-hydroxy-6-methyl-4H-pyran-4-one ring, such as
~
43.66-44.97° and ~ 41.12-41.91°, respectively. Thus, the mononuclear Cu(II) complex 2,
exhibits non planar conformation. In the crystal structure of complex 2, crystallographically
independent molecules of complexes and water molecules are recognized each other through
intermolecular hydrogen bonding via O–H∙∙∙O and N–H∙∙∙O [O–H∙∙∙O = 2.711(2)-2.9594(18)
Å, O–H–O = 155(3)-171(2)°; N–H∙∙∙O = 2.759(2)-2.905(2)Å, N–H–O = 146(2)-158(2)°]
interactions, which leads to the formation of a two dimensional (2D) corrugated hydrogen
bonded sheet (Table 2). Such 2D hydrogen bonded sheets are further packed on top of each
other in an offset fashion, supported by weak intermolecular interactions (Figure 3).
3.4.Hirshfeld surface analysis
Hirshfeld surface analysis was performed to calculate the intermolecular interactions present
in the coordination complexes 1 and 2, and the fingerprint plots were generated using
CrystalExplorer 3.1 [36]. The following equation is used to calculate the normalized contact
distance (dnorm), from the values of de (distance between the Hirshfeld surface and external
molecule), di (distance between the Hirshfeld surface and inside molecule) and Van der waals
radii of the atoms (rivdw or revdw). The resultant value of dnorm, we can identify the regions
participating in the intermolecular interactions in the complexes 1 and 2 [37].
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Moreover by using CrystalExplorer 3.1, we can plot a two dimensional (2D) fingerprint,
which will provide us the summary of the intermolecular contacts in the crystal structure. The
Hirshfeld surfaces of complexes 1 and 2 are shown in Figure 3, in which we have illustrated
various Hirshfeld surface mapping having dnorm, shape index, and curvedness. The inter-
contacts are highlighted by conventional mapping of dnorm on molecular Hirshfeld surfaces as
shown in Figure 4. The red spots over the surface indicate the closeness of atoms to the
Hirshfeld surface to outside, meaning a strong hydrogen bonding between the Hirshfeld
surface and the nearest atoms outside (Figure 4). White and blue color on the surface indicates
the intermediate and little proximity between the atoms involved (Figure 4). In other words,
the major hydrogen bonding interactions such as O–H∙∙∙Cl, N–H∙∙∙N and N–H∙∙∙Cl in 1, and
O–H∙∙∙O and N–H∙∙∙O in 2, involving various functionalities, anion, and solvent in the
complexes, can be seen in the Hirshfeld surface as the red areas (Figure 4). Furthermore, we
have analyzed the contributions of various elements (by plotting a 2D fingerprint) and its inter
contacts to the Hirshfeld surfaces of 1 and 2, which resulted in H∙∙∙H (66.0%), H∙∙∙Cl (10.9%),
C∙∙∙H (6.3%), O∙∙∙H (1.3%) and N∙∙∙H (1.7 %) interactions, for 1, and H∙∙∙H (47.9%), C∙∙∙H
(7.3%), O∙∙∙H (12.2%) and N∙∙∙H (1.4 %) interactions for 2 (Figure 5 and 6). In 1 and 2, there
are two sharp spikes in the lower left area of the fingerprint plot, that are belonged to O–
H∙∙∙Cl/ N–H∙∙∙Cl, and O–H∙∙∙O/ N–H∙∙∙O, respectively (di + de = 2.2 and 1.90 for 1 and 2,
respectively).
3.5. Antioxidant activity
The antioxidant activity of the synthesized ligands (L1 and L2) and their complexes (1 and 2)
has been systematically evaluated using three different assays at different concentration
ranges. The scavenger capacity is determined by measuring the decrease in the absorption of
the DPPH and ABTS radicals, and the results were compared with that of standard
antioxidants including the synthetic antioxidant BHT (Butylated Hydroxy Toluene), ascorbic
acid and Trolox. Meanwhile, we have also evaluated the ability of synthesized compounds to
reduce Fe3+ to Fe2+ by using the Ferric Reducing Antioxidant Power (FRAP) test. These three
assays are mainly used to measure the direct involvement of the compound in improving the
primary antioxidant activity.
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One of the most widely used methods for evaluating total antioxidant activity is the

determination of DPPH
trapping activity by its simple, rapid, sensitive and reproducible
procedure. The DPPH reagent allows us to determine the intrinsic capacity of a substance
having groups (RH) such as phenols to give a hydrogen atom or electrons. In our study (Table
3), Complexes 1 and 2 present a promising free DPPH scavenging capacity with IC50 values
of 45.30 and 72.67 µM, respectively, compared to BHT (4.2 µM).
The ABTS method is based on the ability of hydrogen or electron-donating antioxidants to
decolorize the performed radical monocation of 2,2’-azino-bis(3-ethyl-benzthiazoline-6-
sulfonic acid) generated due to oxidation of ABTS with potassium persulfate. The radical
scavenging abilities showed by the tested compounds towards this assay typically revealed
that, the two complexes 1 and 2 exhibit significantly better activity, expressed as trolox
equivalents (µM Trolox/mM of compound) with 0.31 and 0.50
trolox equivalents,
respectively (Table 3). Whereas, the two ligands L1 and L2 allow the moderate radical
scavenging ability with values 0.13 and 0.07 trolox equivalents, respectively.
Subsequently, we also evaluated the capacity of the synthesized compounds for reducing Fe3+
to Fe2+ by employing the ferric reducing antioxidant power (FRAP) test [33]. The complex 2
displays the higher effect in reducing ferric to ferrous iron, expressed as ascorbic acid (AA)
equivalents (M AA/mM of compound) reaching more than 0.30 ascorbic acid equivalents
(Table 3). Thus, the ligand L1 and complex 1 had moderate effect with 0.14 and 0.19 ascorbic
acid equivalents. However, the complex 2 had a minimum effect in reducing ferric iron, with
value 0.09 ascorbic acid equivalents.
4. Conclusion
Two pyrazole-acetamide ligands (L1[35] and the new L2) were studied for their coordination /
chelation and crystallization properties with CoCl2 and CuSO4, which lead to the formation of
two new mononuclear complexes, [Co(L1)2(EtOH)2]·Cl2 (1) and [Cu(L2)]·H2O (2). Single
crystal X-ray diffraction structural analysis of these two complexes exposed the role of
intermolecular hydrogen bonding interactions, to determine their supramolecular network
topology. The O–H∙∙∙Cl and N–H∙∙∙Cl hydrogen bonding interactions benefits to 1, which is
the first coordination complex with L1, to assemble to form a 1D chain as the primary
supramolecular architecture. C–H∙∙∙π(ring) interaction involving the six membered aromatic
rings allows, 1D chains to be packed in parallel fashion, which resulted in a 2D sheet
structure, with the encapsulation of Cl– within the void space. On the other hand in complex 2,
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O–H∙∙∙O and N–H∙∙∙O hydrogen bonding play a role to self assemble the crystallographically
independent molecules of complexes and water molecules to form a 2D corrugated hydrogen
bonded sheet. Furthermore, the ligands and its complexes were investigated for their
antioxidant activity by examining their in vitro ability to scavenge free radicals such as
DPPH, ABTS and FRAP. The results revealed that the ligands and their complexes exhibited
significant antioxidant capacity compared to literature references.
Abbreviations
AA
Ascorbic acid
ABTS
2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid
Attenuated total reflection
ATR
Butylated Hydroxy Toluene
BHT
Charge-coupled device
CCD
CCDC
DPPH
Cambridge Crystallographic Data Centre
1,1-diphenyl-2-picrylhydrazyl
Dehydroacetic acid
DHA
Electrospray ionization-mass spectrometry
ESI-MS
Ethanol
EtOH
ꢀFRAP
Ferric Reducing Antioxidant Power
Infrared spectrophotometry
IR
Half maximal inhibitory concentration
Nuclear magnetic resonance spectroscopy
Reactive oxygen species
IC50
NMR
ROS
Acknowledgments
This work was supported by a bilateral WBI action with Morocco (COP 22 Program
2018-2022), and the Fonds National de la Recherche Scientifique-FNRS (PDR T.0102.15).
References
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Table 1
Crystallographic and refinement data for 1 and 2
1
2
1853219
CCDC Number
Empirical Formula
Formula weight
Crystal size (mm)
Crystal System
Space Group
a (Å)
b (Å)
c (Å)
 (°)
β (°)
1853218
C28H40CoN8O4Cl2
C20H20CuN4O5
459.9
0.44 x 0.24 x 0.23
Triclinic
682.51
0.41 x 0.18 x 0.14
Triclinic
P1
P1
10.0686(7)
11.5591(8)
17.1250(11)
85.925(1)
78.880(1)
72.506(1)
1865.0(2)
4
8.3807(10)
9.5420(12)
11.0152(14)
73.026(2)
71.246(2)
78.313(2)
792.00(17)
1
γ (°)
V (Å3)
Z
Dcalc. (g/cm3)
F(0 0 0)
1.431
357
0.758
100(2)
1.638
948
1.215
100(2)
MoK (cm–1)
T (K)
Range of h, k, l
θ min/max
Reflections
-11/11, -13/13, -15/15
2.01/29.59
15439/4295/3739
-13/13, -16/15, -23/23
1.85/29.63
36628/10116/9042
collected/unique/observed
Data/restraints/parameters
Goodness-of-Fit (GOF) on F2
Final R indices [I>2σ(I)]
4295/0/198
1.148
R1 = 0.0349
wR2 = 0.0977
R1 = 0.0396
wR2 = 0.0998
10116/0/701
1.044
R1 = 0.0290
wR2 = 0.0754
R1 = 0.0334
wR2 = 0.0775
R indices (all data)
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Table 2
Hydrogen bonding parameters of 1 and 2
1
D–H∙∙∙A
D–H (Å)
H∙∙∙A (Å) D∙∙∙A (Å)
D–H∙∙∙A (°)
Symmetry operation for A
N(2)–H(2)∙∙∙N(4)
0.91
0.87
0.91
0.91
0.91
2.07
2.20
2.24
2.46
2.48
2.9801(18)
3.0575(12)
3.1468(14)
3.2981(13)
3.3779(14)
175
168
175
153
171
1-x, 1-y, 1-z
x, y, z
O(2)–H(2A)∙∙∙Cl(1)
N(3)–H(3A)∙∙∙Cl(1)
N(4)–H(4A)∙∙∙Cl(1)
N(4)–H(4B)∙∙∙Cl(1)
1-x, -y, 1-z
x, y, z
2-x, -y, 1-z
2
N(1)–H(1)∙∙∙O(9)
0.80(2)
0.81(3)
0.84(3)
0.86(3)
0.84(3)
0.79(3)
0.98(2)
0.92(2)
0.90(2)
2.21(2)
1.99(3)
1.92(3)
2.16(3)
1.88(3)
2.04(3)
2.29(2)
2.52(2)
2.57(2)
2.905(2)
146(2)
1-x, 1-y, 1-z
1+x, y, z
-x, 1-y, 1-z
1-x, -y, 1-z
x, y, z
N(5)–H(5)∙∙∙O(10)
O(9)–H(9A)∙∙∙O(1)
O(9)–H(9B)∙∙∙O(6)
O(10)–H(10A)∙∙∙O(5)
O(10)–H(10B)∙∙∙O(1)
C(25)–H(25B)∙∙∙O(2)
C(31)–H(31)∙∙∙O(7)
C(39)–H(39)∙∙∙O(5)
2.759(2)
158(2)
2.7508(19)
2.9594(18)
2.711(2)
171(2)
155(3)
170(3)
2.830(2)
171(3)
x, y, z
3.1658(19)
3.432(2)
147.8(17)
170.3(17)
161.4(18)
x, -1+y, z
2-x, -y, -z
1+x, y, z
3.432(2)
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Table 3
Antioxidant activity of L1, L2, 1 and 2
DPPH
ABTS
µM ET/mM
0.13 ± 0.01
0.07 ± 0.01
0.31 ± 0.02
0.50 ± 0.01
-
FRAP
µM EAA/mM
0.14 ± 0.01
0.09 ± 0.02
0.19 ± 0.01
0.30 ± 0.02
-
IC50 (µM)
L1
L2
1
NA
NA
72.67 ± 4.10
45.30 ± 4.49
4.20 ± 0.02
2
BHT
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Scheme 1. Synthetic routes of L1 and L2.
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Figure Captions
Figure 1. N-(2-aminophenyl) -2- (5-methyl-1H-pyrazol-3-yl) acetamide (L1) and (E)-N-(2-
(1-(2-hydroxy-6-methyl-4-oxo-4H-pyran-3-yl)ethylideneamino)phenyl)-2-(5-
methyl-1H-pyrazol-3-yl) acetamide (L2).
Figure 2: Crystal structure description of 1, a) Crystal structure of the coordination complex
showing the coordination environment; b) One dimensional (1D) hydrogen
bonded chain supported by O–H∙∙∙Cl and N–H∙∙∙Cl interactions, displaying the
inclusion of Cl– anion; the parallel packing of 1D hydrogen bonded chains in ball
and stick fashion c) and spacefill model d), (the adjacent chain are shown in red,
blue and orange color, Cl– is shown in green color).
Figure 3: Crystal structure description of 2, a) Crystal structure of the coordination complex
showing the square planar coordination geometry; b) the packing of
crystallographically independent molecules of complexes (shown in blue and red
color) and occluded water (shown in magenta and green); 2D hydrogen bonded
network, formed by the self-assembly of crystallographically independent
molecules of complexes and water along crystallographic axis “c” (c) and “a” axis
(d); e) offset packing of 2D sheets.
Figure 4: Hirshfeld surface mapped having dnorm (left), shape index (middle), and curvedness
(right) of 1 (a) and 2 (b).
Figure 5: The 2D fingerprint plots for 1
Figure 6: The 2D fingerprint plots for 2
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Figure 1
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Figure 2
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Figure 3
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Figure 4
a)
b)
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Figure 5
H…Cl 10.9%
C…H/H…C 6.3%
N…H/H…N 1.7%
H…H 66%
O…H/H…O 1.3%
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Figure 6
C…H/H…C 7.3%
N…H/H…N 1.4%
O…H/H…O 12.2%
H…H 47.9%
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Graphical abstract
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Highlights
 Synthesis of new pyrazole-acetamide derivatives and two coordination
complexes
 X-ray Single crystal structure description of these complexes
 Study the impact of supramolecular bonding on crystal packing of these
complexes
 In vitro study of antioxidant activity of ligands and their complexes.
28